The invention relates to a method for monitoring functional states of a pressure-driven actuator, and to a pressure-drivable actuator.
One field of application concerns vacuum-driven actuators, e.g. vacuum pick-up devices, expansion bellows or vacuum tube lifters comprising vacuum lifting tubes, as described e.g. in WO 2005/110907 A1 or U.S. Pat. No. 4,413,853 A. Another field of application concerns overpressure-driven actuators, e.g. pneumatic or hydraulic actuators or manipulators.
Actuators of this type have in common that pressure is applied to a flexibly deformable actuator compartment in order to actuate the actuator. In this case, in principle this may relate to overpressure (for overpressure-driven actuators) or a vacuum (for vacuum-driven actuators). Pressure is applied to the actuator compartment in particular by means of a working fluid, which is provided by an operating pressure supply (e.g. a pressure source, vacuum pump, ejector or the like). The working fluid may in principle have an overpressure or a vacuum relative to the surroundings. The working fluid may e.g. be a hydraulic fluid or a compressed gas, such as compressed air. The present invention relates in particular to pneumatic actuators using air as the working fluid.
Said actuators are usually intended to be integrated in more complex handling processes or production processes in which an object needs to be e.g. lifted, gripped, clamped, processed or handled in another way. In particular, automated processes are desired. This makes it possible for the individual functional units to be operated as required and such that they are coordinated with one another.
To do this, the functional state of an actuator is intended to be monitored during its operation. In particular, functional data is intended to be determined which represent the functional state and e.g. relate to the current operating state, configuration, load state or the like of the actuator.
There are many different factors influencing this characteristic information. First of all, the mechanical properties of the actuators may change over time, e.g. due to ageing or wear of the materials used. Likewise, the hydromechanical properties of the working fluid may change over time. In addition, the current functional state of an actuator itself has an influence on the measurable characteristic variables. For example, the current compression state of the actuator compartment and/or the current deformation state of the actuator compartment influences the response of said compartment when a pressure change is applied.
In order to obtain reliable and significant information regarding the functional states of the individual units in a more complex system, it is known to assign sensors that monitor various properties to each of the various pressure-drive or pressure-controlling units. For example, a supply pressure of a vacuum pick-up device can be monitored (e.g. DE 10 2014 206 308 A1) or the compressed supply air fed to a compressed-air-driven ejector can be monitored (e.g. WO 2013 120801 A1). It is also known to use sensors to monitor when the relevant starting configurations or end configurations of an actuator have been reached. In order to monitor various types of functional state, a plurality of sensors comprising associated data communication and control are required, and this can lead to increased structural complexity and increased susceptibility to errors.